Need For Less Sleep Associated with Gene Mutation

Researchers at the University of California, San Francisco, have discovered the first gene involved in regulating the length of human sleep. The study, published recently in the journal Science, identified a genetic mutation that is associated with a short human sleep phenotype [1]. The finding may help scientists better understand the regulatory mechanisms of sleep and lead to treatments for a variety of sleep disorders.

Researchers identified a small extended family with two individuals who had lifelong shorter daily sleep times than normal individuals (self-reported average of 6.25 hours vs. 8.06 hours). DNA sequencing identified a point mutation in the gene DEC2 (Differentially expressed in chondrocytes protein 2) (chondrocytes are the only cells found in cartilage, the connective tissue within joints). In mice, DEC2 has been previously identified as a component of the mammalian circadian clock (the ~24-hour wake-sleep cycle), repressing the expression of other circadian clock genes [2]. In vitro tests showed that the human mutation reduced the repressive activity of DEC2.

To examine the effect of the mutation, scientists generated DEC2 transgenic mice (meaning a mouse with a segment of DNA that originated in a different species, in this case two copies of the human DEC2 gene, one containing the point mutation and one normal copy). Studies showed that these mice slept less compared to controls. To study sleep directly, electroencephalography (EEG) and electromyography (EMG) tests were performed. The results suggest that the DEC2 point mutation does not affect the depth of sleep. Rather, the sleep structure of mice containing the DEC2 point mutation appeared more fragmented than that of normal mice, particularly non-rapid eye movement (NREM) sleep (about 80% of sleep is spent in dreamless NREM sleep). Further studies found that mice with the mutation also recovered quicker from periods of sleep deprivation compared to normal mice.

Studies were then done in fruit-flies expressing either the normal mouse Dec2 gene or the mouse Dec2 gene containing the point mutation. Flies expressing the mouse Dec2 gene containing the point mutation showed significantly lower daytime sleeplike behavior compared with flies expressing the normal mouse Dec2 gene. Thus, the shortened sleep effect of the DEC2 point mutation was replicated in both mouse and fruit-flies.

What’s interesting about this study is that a genetic mutation can lead to a behavioral trait, not just an observable characteristic.

How much is too little or too much sleep? There is no magic number. Different age groups need different amounts of sleep, but sleep needs are also individual. Generally speaking, research shows that most adults need 7-9 hours of sleep, while younger children need as much as 10-14 hours [3]. For more information on the importance of sleep as well as sleep-related problems, visit the National Sleep Foundation (NSF).